1. Field of the Invention
This invention relates to a vacuum skin package comprising a gas permeable film having specific permeability requirements. This invention particularly relates to improved packaging structures for perishable food products.
2. Description of the Related Art
Perishable food products are subject to contamination when exposed to microbial organisms such as bacteria, molds and the like. Contamination can result in accelerated spoilage, toxin formation and other harmful effects. Packaging such perishable goods in gas impermeable materials such as foil, coated paperboard and oxygen barrier films can provide a barrier to microbial contamination. However, anaerobic organisms such as C. botulinum, which produces a potent toxin that is the causative agent of botulism, thrive in oxygen-depleted atmospheres. Gas impermeable materials such as foil, paperboard and oxygen barrier films are not suitable to package goods highly susceptible to botulin toxin formation.
C. botulinum contamination is particularly problematic in fresh fish. Packaged fresh fish is typically frozen for this reason. To avoid problems associated with storing, shipping and merchandising fresh fish, packages suitable for protecting fresh fish can be desirable.
Vacuum packaging is a process used to protect perishable items from deterioration wherein a vacuum is applied to a package to actively remove air to conform the packaging film to the shape of the content prior to sealing the package. Skin packaging is a known technique where goods are tightly packaged within a wrapping material and where substantially all of the atmospheric air is excluded. Vacuum skin packaging is a combination of the two packaging processes. However, conventional packaging of this type excludes oxygen and therefore does not inhibit the growth of C. botulinum. 
It has been known to include certain gases in packaging to enhance the storage stability of the contents and increase the shelf life. Packages can be made with gas impermeable materials if oxygen is available in the headspace of the package to inhibit growth of anaerobic organisms. However, it is difficult to provide sufficient oxygen in the headspace of such a package to provide extended protection against growth of anaerobes.
The U.S. Food and Drug Administration (FDA) guidelines state that packages having an oxygen transmission rate (OTR) greater than or equal to 10,000 cc/m2/24 hr meets the guidelines for being “oxygen permeable”. Unless a package is considered oxygen permeable by the FDA a “Hazard Analysis of Critical Control Points” (HACCP) plan must be established. Under a HACCP plan temperature monitoring is required and time/temperature indicators (TTI's) must be provided on shipping containers. Temperature monitoring protocols alone may not be sufficient in protecting food from spoilage. A further problem is that meeting the FDA OTR guidelines is not possible using conventional foam trays currently used to package foodstuffs such as fresh meats.
To add to the complexity of packaging perishable foods such as fish, it can be desirable to maintain the moisture level in the food. Fish can be packaged in trays with raised areas for the fish to rest on, allowing oxygen to contact the bottom of the fish. However, trays of this type allow liquid to drain from the fish. Films having high moisture permeability allow moisture to escape from the package, resulting in dehydration of the product and lower quality.
U.S. Pat. Nos. 4,685,274; 4,840,271; 5,025,611; 5,103,618 and 5,115,624 describe packages, methods, and apparatuses for packaging perishable goods. U.S. Pat. App. Pub. 2003/0198715 A1 discloses films and packages of highly neutralized blends of organic acids and ethylene acid copolymers having good oxygen permeability.
It can be desirable to prepare packages having high oxygen permeability and low moisture permeability for packaging perishable food items.